The present invention generally relates to an image forming apparatus such as a copying machine, and more particularly to an image forming apparatus employing an intermediate tray to form images on both sides of a copy sheet.
Conventionally, there have been widely used copying machines which are adapted to optically scan an image of a document original placed at an image forming position on a contact glass; to form an electrostatic latent image corresponding to the image of the document original thus scanned on a photoconductive material; to develop the electrostatic latent image into a toner image; and then to transfer the resultant toner image onto a copy sheet. Such copying machines typically allow the selection of image forming modes which include: (a) one-side copy modes such as mode wherein an image of a one-sided document original is reproduced on one side Of a copy sheet, and a mode wherein images of a two-sided document original are reproduced on one side of each copy sheet; and (b) two-side copy modes such as mode wherein images of one-sided document originals are reproduced on both sides of a copy sheet respectively, and a mode wherein images of a two-sided document original are reproduced on both sides of a copy sheet.
In the two-side copy mode of (b), after an image is reproduced on one side of a copy sheet, another image must be reproduced on the other side of the copy sheet, and therefore, copy sheet with an image reproduced on one side thereof is stored by an intermediate tray within the main body of a copying machine, from which the copy sheet thus stored is taken out so that another image may be reproduced on the other side thereof.
Unfortunately, the copying machine is restricted in the number of sheets to be stored by the intermediate tray, which determines the number of copy sheets to have images formed on both sides thereof in the two-side copy mode.
For example, if 120 two-sided copies are to be produced from one document original by the use of an intermediate tray having the capacity of storing 100 sheets, it is impossible to produce all the 120 copies at a time because the intermediate tray cannot receive as many as 120 sheets.
In this case, the prior art machines are arranged such that the keyboard for setting the number of copies to be produced does not permit the setting of the number of copies which exceeds the storing capacity of the intermediate tray.
Consequently, it was impossible to produce a large volume of two-sided copies at a time.